$\begin{array}{1 1}\text{(a)the impact of a falling raindrop creates a small crater in the soil,ejecting soil particles}\\\text{(b)the development of small, ephemeral concentrated flow paths which function as both sediment source and sediment delivery systems for erosion on hillslopes} \\ \text{(c)occurs when runoff water accumulates and rapidly flows in narrow channels during or immediately after heavy rains or melting snow, removing soil to a considerable depth} \\
\text{(d)the transport of loosened soil particles by overland flow} \end{array}$